INDIVIDUAL NEURONS DISSOCIATED FROM RAT SUPRACHIASMATIC NUCLEUS EXPRESS INDEPENDENTLY PHASED CIRCADIAN FIRING RHYTHMS

Within the mammalian hypothalamus, the suprachiasmatic nucleus (SCN) c ontains a circadian clock for timing of diverse neuronal, endocrine, a nd behavioral rhythms. By culturing cells from neonatal rat SCN on fix ed microelectrode arrays, we have been able to record spontaneous acti on potentials from individual SCN neurons for days or weeks, revealing prominent circadian rhythms in firing rate. Despite abundant function al synapses, circadian rhythms expressed by neurons in the same cultur e are not synchronized. After reversible blockade of neuronal firing l asting 2.5 days, circadian firing rhythms re-emerge with unaltered pha ses. These data suggest that the SCN contains a large population of au tonomous, single-cell circadian oscillators, and that synapses formed in vitro are neither necessary for operation of these oscillators nor sufficient for synchronizing them.